Nucleic acid repeats are associated with various diseases. For example, expansion of a CGG triplet repeat sequence in the 5′ UTR of the FMR1 gene (OMIM *309550) is associated with fragile X syndrome (FXS, OMIM #300624), the most common inherited form of mental retardation. Expansion of this repeat into the full mutation range (≥200 repeats) triggers methylation and transcriptional silencing of FMR1, causing FXS. In the “normal” range (5-44 repeats), the repeat sequence is stable between generations; intermediate alleles (45-54 repeats) require at least two generations to expand to full mutations, and premutation alleles (55-200 repeats) may expand to full mutations when passed from a mother to her child. Due to the difficulty of amplifying long triplet repeats, traditional tests for FXS carrier status have relied on Southern blotting to detect expanded CGG repeats. Recent advances in polymerase chain reaction (PCR) methods allow detection of these repeats with accuracy and sensitivity equal to Southern blotting. Capillary electrophoresis of the PCR product makes it possible to quantify the CGG repeat count, but requires laborious peak-calling and counting.